The present invention relates to a tool-positioning method and a tool-positioning device, for positioning the tip end of a tool relative to the center axis of a bar. The present invention also relates to a power feeder for tool positioning, that can be used for positioning the tip end of a tool relative to the center axis of a bar.
For machining an external peripheral surface of a bar-shaped workpiece (hereinafter referred to as a bar) with a lathe, the machining work is usually started after the tip end of a tool, such as a turning tool, mounted on a tool rest, is positioned in relation to a center line or axis of the bar. For example, in a case where a tool rest (hereinafter referred to as a flat turret) for supporting a plurality of tools in a parallel arrangement is installed on a machine tool (hereinafter referred to as an automatically operated lathe), such as an NC lathe, capable of automatically carrying out various kinds of machining processes including mainly turning, the flat turret is usually structured to be able to move in parallel in rectangular two-axis directions (e.g., X-axis and Y-axis directions) within a plane orthogonal to the center axis of a bar securely held in a rotary spindle. In this structure, for machining the bar with a desired tool, the target position or path of the tip end of the tool is set on X-Y coordinates, while the positional coordinates of the center axis of the bar in the X-Y coordinate system on the lathe bed are considered as a reference or origin.
At the time of selecting a tool, for example, the flat turret is moved in parallel or translated in the Y-axis direction (along the parallel array of the tools), at a location where the tip ends of tools mounted on the flat turret are not brought into contact with the bar. Then, at the instant when the tip end of the desired tool to be selected has been aligned with the center axis of the bar in the X-axis direction, the selection of the tool is completed. From this position, the flat turret is moved in parallel in the X-axis direction, and the tip end or nose of the selected tool is abutted with the bar to start the machining. In the case where the selected tool is a turning tool, for example, the X-axis feed rate of the flat turret is controlled so as to determine a cut depth by the turning tool on the bar as well as a setback or standby position of the nose during a non-use period of the turning tool. It should be noted that the term xe2x80x9cthe tip end of a toolxe2x80x9d or xe2x80x9cthe nose of a toolxe2x80x9d in this specification shows a portion of the tool, that is first brought into contact with the bar for starting the machining.
The above-described feed motions of the flat turret in the Y-axis direction (at the time of selecting a tool) and in the X-axis direction (at the time of machining) are carried out in accordance with the predetermined coordinate data for the position of the tool selected on the flat turret and for the target position of the tip end of the selected tool during the machining work. Therefore, in order to perform high precision machining, it is necessary that the positional coordinate data of the selected tool has been set accurately in relation to the center of the bar as reference, regardless of the kind of the selected tool. However, depending on the differences between the nose shapes and/or the tip-end abrasion levels of the selected tools, the actual move position of the tool nose may be deviated from the predetermined coordinates, even when the flat turret has been fed properly in accordance with the predetermined data. In order to eliminate such an inconvenience, it is required to correct the predetermined coordinate data of each tool before starting the machining work. In this respect, the meaning of the term xe2x80x9cpositioningxe2x80x9d in this specification includes such a correction of the predetermined coordinate data.
Such a preliminary positioning operation of tools is usually performed each time when the tools are replaced with each other, in the typical case where a plurality of tools are used for machining one bar. Therefore, it is advantageous to automatically perform the positioning operation under a predetermined control flow, as a preparatory step in a sequence of automatic machining works in an automatically operated lathe. For example, Japanese Unexamined Patent Publication (Kokai) No. 8-118103 (JP-A-8-118103) discloses a device for automatically performing the above-described positioning operation of the tip end of a tool prior to the machining work.
This known device includes tool abutting means for bringing a turning tool into contact with an external peripheral surface of a bar, contact-position deciding means for deciding a position of contact between the bar and the turning tool, and processing or operating means for calculating a position of a center axis of the bar on the basis of the decided contact-position data. The tool abutting means sequentially brings the nose of a turning tool into contact with at least three different positions in peripheral and axial directions on the external peripheral surface of the bar in rotation, and at each time of contact, the contact-position deciding means decides a position of contact. Then, the processing means determines a position of the center axis of the bar (i.e., a calculated center value) on the basis of at least three contact-position data of the turning tool nose thus decided. The turning tool is fed to a position set in relation to this calculated center value as reference. When the turning tool is replaced or changed with another one, a calculated center value is determined for the next turning tool in the same procedure as described, and the old calculated center value is re-written at each time of the tool change.
According to the above conventional device for positioning the tip end of a tool, the contact position is decided by directly abutting the nose of the turning tool onto the external peripheral surface of the rotating bar, so as to determine the calculated center value of the bar. Therefore, before the machining of the bar is started, the external peripheral surface of the bar is cut slightly. Even when the bar is not rotated, there is a risk that the external peripheral surface of the bar is damaged by the nose of the turning tool. It is thus required to abut the nose onto the bar at a position permitting such a cutting or damage, so that it becomes essential to select the position of contact with the tool. Further, there is a risk of abrasion or damaging of the nose of the turning tool, during the positioning of a tool tip end as a preparatory step of the machining work, which may shorten the life of the turning tool in the actual machining work.
It is, therefore, an object of the present invention to provide a tool-positioning method and a tool-positioning device, capable of easily and accurately positioning the tip end of a tool relative to the center axis of a bar without damaging the external peripheral surface of the bar and/or the tool in itself.
It is another object of the present invention to provide a power feeder or excitation device for tool positioning, capable of being used for the positioning operation of a tool and capable of preventing the external peripheral surface of a bar and/or the tool in itself from being damaged.
In order to achieve the above objects, the present invention provides a tool-positioning method for positioning a tip end of a tool relative to a center axis of a bar, comprising providing a flexible strip member having a conducting front side and an insulating back side; fixedly disposing a bar to be machined at a machining work position, and wrapping the strip member on an external peripheral surface of the bar with the back side being closely attached to the external peripheral surface; bringing a tool to be positioned into contact with the front side of the strip member; detecting a conduction between the tool and the front side of the strip member at a time of a mutual contact, to decide a position of a contact point with the tool; and determining a position of a tip end of the tool during a machining, on the basis of the position of the contact point with the tool as decided.
In this tool-positioning method, the determining of a position of a tip end of the tool may include a work of determining a position of a center axis of the bar to be machined on the basis of the position of the contact point with the tool as decided, and a work of suitably correcting predetermined machining-position data of the tool in accordance with the position of the center axis of the bar as determined.
Alternatively, the determining of a position of a tip end of the tool may include a work of mechanically positioning the tip end of the tool relative to a center axis of the bar to be machined, on the basis of the position of the contact point with the tool as decided.
The present invention also provides a tool-positioning device for positioning a tip end of a tool relative to a center axis of a bar, comprising a flexible strip member having a conducting front side and an insulating back side; a wrapping mechanism for keeping the strip member wrapped on an external peripheral surface of a bar to be machined, the bar being fixedly disposed at a machining work position, with the back side of the strip member being closely attached to the external peripheral surface; a driving mechanism for bringing a tool to be positioned into contact with the front side of the strip member; a power feeding mechanism for allowing an electric current to flow between the tool and the front side of the strip member at a time of a mutual contact; a contact-position deciding section for detecting a conduction between the tool and the front side of the strip member caused due to the power feeding mechanism, to decide a position of a contact point with the tool; and a corrective processing section for determining a position of a center axis of the bar on the basis of the position of the contact point with the tool as decided, and suitably correcting predetermined machining-position data of the tool in accordance with the position of the center axis of the bar as determined.
In this tool-positioning device, it is advantageous that the tool is mounted on a tool rest of an automatically operated lathe, and the driving mechanism comprises a tool-rest driving mechanism in the automatically operated lathe.
Also, the contact-position deciding section and the corrective processing section may include a controlling section in an automatically operated lathe.
The present invention further provides a tool-positioning device for positioning a tip end of a tool relative to a center axis of a bar, comprising a flexible strip member having a conducting front side and an insulating back side; a wrapping mechanism for keeping the strip member wrapped on an external peripheral surface of a bar to be machined, the bar being fixedly disposed at a machining work position, with the back side of the strip member being closely attached to the external peripheral surface; a driving mechanism for bringing a tool to be positioned into contact with the front side of the strip member; a power feeding mechanism for allowing an electric current to flow between the tool and the front side of the strip member at a time of mutual contact; a contact-position deciding section for detecting a conduction between the tool and the front side of the strip member caused due to the power feeding mechanism, to decide a position of a contact point with the tool; and a positioning member for mechanically positioning a tip end of the tool relative to a center axis of the bar to be machined, on the basis of the position of the contact point with the tool as decided.
In this tool-positioning device, it is advantageous that the tool is mounted on a tool rest of an automatically operated lathe, and the driving mechanism comprises a tool-rest driving mechanism in the automatically operated lathe.
Also, the contact-position deciding section may include a controlling section in an automatically operated lathe.
Also, the positioning member may comprise a holder for fixedly supporting the tool, and a spacer mounted on the holder for determining a position of the tool.
The present invention yet further provides a power feeder for tool positioning, for positioning a tip end of a tool relative to a center axis of a bar, comprising a flexible strip member having a conducting front side and an insulating back side; a wrapping mechanism for keeping the strip member wrapped on an external peripheral surface of a bar, with the back side of the strip member being closely attached to the external peripheral surface; and a power feeding mechanism electrically connected to the front side of the strip member.
In this power feeder, it is preferred that the strip member has an annular shape.
Also, it is advantageous that the wrapping mechanism includes a tension unit for applying tension to the strip member.
It is also advantageous that the wrapping mechanism includes a guide unit for closely attaching the strip member to a portion of the external peripheral surface of the bar over a central angle of 180 degrees or above.
Alternatively, the wrapping mechanism may include an adhesive for detachably adhering the back side of the strip member to the external peripheral surface of the bar.
The power feeder is capable of being detachably installed on a spindle stock of an automatically operated lathe.
In this arrangement, the power feeding mechanism preferably includes an electrode member contacting with the front side of the strip member and insulated from the spindle stock.